How to use Tar in Linux

Tar, short for tape archive, is an archive format commonly used in Linux for bundling and organizing files and directories. In this article, I'll go over the basics needed to get started using this utility.

About the Tar Format

Tar files have a simple structure. They consist of a series of file entries concatenated together. Each file entry represents a file or directory and contains metadata about the file, such as:

• name
• permissions
• owner
• group
• timestamp
• file size

The structure of a file entry typically includes the following components:

1. Header: The header section contains information about the file, including its name, permissions, timestamps, owner, group, file size, and other metadata. The header is a fixed-size block that precedes each file entry.

2. File Data: Following the header is the actual file data, which represents the content of the file. The file data section varies in size depending on the file's size.

3. Padding: Tar files use padding to align file data on block boundaries. Padding ensures that each file entry occupies a multiple of a specific block size, typically 512 bytes.

4. End of File Markers: Tar files often end with two empty 512-byte blocks, indicating the end of the archive.

Creating a Tar File

To create a Tar file, use the tar command with the -cvf flags followed by the desired name of the Tar file and the files or directories to include. For example, to create a Tar file named backup.tar containing two files named contacts.txt and config.txt, run the following command:

tar -cvf backup.tar contacts.txt config.txt

Let's have a look at the flags:

• -c (or --create) tells tar to create a new archive.
• -v (or --verbose) tells tar to display detailed information about the files being processed. When used with the -c flag, the verbose mode shows the names of the files being added to the archive.
• -f (or --file) tells tar the file name or device where the Tar archive will be stored. This flag is necessary when creating or manipulating Tar files.

Extracting Files From a Tar File

To extract the contents of a Tar file, use the tar command with the xvf flags followed by the name of the Tar file. For example, to extract the file created in the previous section, run the following command:

tar -xvf backup.tar

The -x (or --extract) tells tar to extract the files from the Tar archive.

By default, the files will be extracted in the current working directory.

To specify a different extraction directory, use the -C (or --directory) flag followed by the desired path. For example, to extract the files to the home directory, run the following command:

tar -xvf backup.tar -C ~/

Tar File Compression

A Tar file is effectively the result of concatenating multiple file entries, each containing metadata and file data, in a structured format. To save on disk space, this file can be compressed using various compression algorithms such as GZIP or BZIP2, resulting in a compressed Tar archive.

For example, to create a compressed Tar file, the tar command can be combined with the gzip command:

tar -cvf backup.tar contacts.txt config.txt | gzip > backup.tar.gz

However, there is an easier way to do this. When creating a Tar file, use the -z flag to tell tar to use GZIP compression. For example, this command will result in the same output as the command above:

tar -cvzf backup.tar.gz contacts.txt config.txt

Similarly, to use BZIP2 compression, use the -j flag:

tar -cvjf backup.tar.bz2 contacts.txt config.txt

To decompress a Tar file, the tar command can automatically detect the compression format used from the file name extension. For example:

tar -xf backup.tar.gz

In this case, the tar command recognizes the .tar.gz extension and automatically applies the appropriate decompression (in this case, GZIP) before extracting the files.

If a Tar file does not have an extension, the compression format cannot be determined solely based on its name. In these cases, the tar command needs to be provided with the appropriate compression flag. For example, to extract a Tar file named backup compressed using GZIP, use the following command:

tar -xzf backup

Inspecting a Tar File

To see the contents of a Tar file, use the tar command with the -tf flag. The -t (or --list) flag tells tar to list the contents of the Tar file without extracting them. For example, to see the contents of Tar file from the previous examples, run the following command:

tar -tf backup.tar

Adding to a Tar file

It is possible to append additional files or directories to an existing Tar file. For example, the following command will append the file numbers.txt to backup.tar.

tar -rf backup.tar numbers.txt

The -r (or --append) flag tells tar to append the files and directories provided to the end of the Tar file.

Keep in mind that this operation is only appending a new file entry to the end of the Tar file. When a file being appended has the same name as one already in the Tar file, the latest one will be used by default. But the Tar file will contain both versions.

To extract a specific occurrence, use the tar command with the --occurrence flag. For example:

tar -xf backup.tar --occurrence=2 numbers.txt

In this case, the --occurrence flag is used to tell tar to process the second occurrence of the file numbers.txt in backup.tar.

Conclusion

The tar command has many more options that I won't explore here. But this should be enough to get started using Tar in Linux.